Prior art methods are known for the recovery of polyester from cotton fabrics and from photographic film waste, which involve dissolution of the polyester in various solvents, followed by precipitating and recovering the polyester.
U.S. Pat. No. 5,342,854, issued on Aug. 30, 1994, describes a process for recovering polyester from a polyester/cotton blend fabric by dissolving the polyester in an alkyl sulfone solvent, separating the dissolved polyester and alkyl sulfone solvent solution from the cotton fabric and precipitating the polyester from the alkyl sulfone solvent solution.
British Patent 1,548,043, published on Jul. 4, 1979, describes a process for obtaining polyethylene terephthalate (PET) powder from PET textile waste by dissolving the PET in a halogenated hydrocarbon solvent at a temperature of up to 200.degree. C. at the vapor pressure of the solvent and cooling the PET solvent solution to precipitate the PET powder.
British Patent 1,518,211, published on Jul. 19, 1978, describes a process for recovering silver value from photographic film waste, which waste comprises silver halide and/or metallic silver, a layer of polyester base film and a subbing layer of polyvinyl-idenechloride. The photographic waste is dissolved in an aromatic ether solvent, such as anisole, phenetole or benzyl ether, the silver value is separated by filtration and the solvent phase is subsequently cooled to precipitate the PET while maintaining the polyvinyl-idenechloride in solution.
Technical, economic and environmental considerations due to the solvent systems used in the prior art processes dramatically limit their applicability to laboratory scale investigations. Such solvent systems have very limited commercial applications.
The process of the present invention provides an effective, reliable and economical means for recovering a polyester, particularly polyethylene terephthalate (PET), from contaminated polyester waste such as a polyester and cotton blend fabric, a polyester magnetic tape, or other contaminated polyester waste. Advantageously, the polyester can be recovered by crystallization, filtration and solid state processed to an appropriate molecular weight. Alternatively, the dissolved polyester can be utilized directly as a feedstock for methanolysis to recover dimethyltere-phthalate (DMT) and alkylene glycol. The DMT can subsequently be hydrolyzed to recover terephthalic acid (TPA).